Composite wire and wire coil adapted for use in fabricating multiply-coiled electrodes



May 31, 1966 T. H. HEINE 3,253,894

COMPOSITE WIRE AND WIRE COIL ADAPTED FOR USE IN FABRICATING MULTIPLY-COILED ELECTRODES Original Filed Jan. 12, 1962 2 Sheets-Sheet 1 INVENTOR. THO/7H5 H. Hf/NE.

May 31, 1966 T. H. HEINE 3,253,894

COMPOSITE WIRE AND WIRE COIL ADAPTED FOR USE IN FABRICATING MULTIPLY-COILED ELECTRODES Original Filed Jan. 12, 1962 2 Sheets-Sheet 2 FIG.9. FIG. IO.

INVENTOR. THO/VH5 HE/NE.

United States Patent COMPOSITE WIRE AND WIRE COIL ADAPTED FOR USE IN FABRICATING MULTIPLY-COILED ELECTRODES Thomas H. Heine, Cedar Grove, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Original application Jan. 12, 1962, Ser. No. 165,884. Divided and this application June 3, 1965, Ser. No.

6 Claims. (Cl. 29-190) This application is a division of copending application Serial No. 165,884, filed January 12, 1962.

This invention relates to electrodes for, electric discharge devices and, more particularly, to a composite wire and a wire coil adapted for use in making a multiplycoiled electrode for a fluorescent lamp.

The design of fluorescent lamp cathodes, particularly those for so-called rapid and instant start lamps, presents an especially diflicult problem in that such cathodes require a fine wire winding that heats up rapidly and the electrode per se must have a mass large enough to avoid localized overheating and sputtering. In addition, the electrode structure must be capable of holding a suflicient amount of electron-emission material to enable the lamps to have a long useful life.

The aforesaid stringent requirements are satisfied in the case of rapid and instant-start fluorescent lamps by utilizing an electrode that includes both a fine wire or socalled filament winding and a winding of much heavier wire. The fine wire is first wound around the heavier core wire and the resultant composite wire is then wound into a coil. This coil is, in turn, wound into a still larger coil to provide what is commonly referred to in the art as a triple-wound electrode. In reality, however, only the fine wire overwinding is triply coiled and the heavier wire is doubly coiled.

The desired large carrying capacity for emission mate rial is obtained by pairing a temporary filler wire with the core wire before the fine wire winding is applied and, after the subsequent coiling operations have been completed, chemically dissolving the filler wire and removing it from the coil structure. The fine wire accordingly is loosely draped around the core Wire resulting in an electrode having a basket-like structure that can hold surprisingly large amounts of emission material. A triplewound electrode of this character and the manner in which it is conventionally fabricated is disclosed in US. Patent No. 2,306,925, issued December 29, 1942, to J. O. Aicher.

Such triple-wound electrodes are diflicult to'rnanufacture and are expensive because the percent shrinkage during production is rather high. A large portion of the shrinkage arisesfrom a defect known as abrasion. This term refers to the flattening and/or erosion of the fine wire which occurs as the core wire on which it is wound passes over the wire guides of the coil-winding machines and is subsequently wound around the mandrels during the secondary and tertiary winding operations. The abrasion is frequently severe enough to cause the fine overwinding to break. When this occurs large numbers of coils must be discarded insofar as the small hooks formed at the break causes the coils to become inseparably tangled, or the break allows the fine overwinding to become separated from the primary mandrel.

Moreover, experience has shown that the degree of abrasion increases as the diameter of the filament wire is decreased, or the diameter of the core wire is increased. Insofar as the highly-loaded high-wattage fluorescent lamps now being marketed require cathodes with finer filament wires and larger core wires, the resultant severity of the abrasion problem has made it extremely difiicult to make cathodes for such lamps at a reasonable cost.

It is accordingly the general object of this invention to provide a composite wire that includes a fine filamentary wire and can be wound into a coil without materially damaging the fine wire.

A more specific object is the provision of a composite wire that can be formed into a triple-wound cathode for a fluorescent lamp with a minimum amount of shrinkage and defects.

Another object is the provision of a wire coil that can be manufactured at minimum cost and conveniently converted into a finished triple-wound fluorescent lamp cathode free from major imperfections.

The aforesaid objects, and additional advantages which will appear as the description proceeds, are achieved in accordance with this invention by winding a larger wire along with the fine wire around the primary mandrel during the initial coiling operation and subsequently removing the larger wire from the finished coil. This larger wire, by virtue of its larger diameter, 'serves as a buffer wire that protrudes beyond the fine wire and thus provides a temporary bearing surface that protects the fine wire from abrasion by the wire guides and mandrels during the subsequent coiling operations. The combination of such a buffer wire with a pair of fine tungsten wires which are wound simultaneously as a group around the primary mandrel affords the additional advantages of decreasing the winding time and amount of buffer wire required, and maintaining a very uniform spacing between the fine wire turns in the finished electrode.

Partly fabricated triple-wound coils containing a buffer wire winding of molybdenum or the like constitute a useful intermediate article of manufacture in that the coils can be readily handled and bulk shipped in this condition and then readily converted into finished electrodes simply by immersing the coils in an acid bath that dissolves the buffer wire.

A better understanding of the invention will be obtained by referring to the acompanying drawings, wherein:

FIGURE 1 is a perspective view of a mount for a 212 watt 96" highly-loaded fluorescent lamp which includes a triple-wound cathode manufactured in accordance with this invention;

FIG. 2 is an enlarged side elevational view of the primary mandrel and coiling operation in accordance with one form of the invention;

FIG. 3 is a cross-sectional view through the primary mandrel and winding along the line III-III' of FIG. 2, in the direction of the arrows;

FIG. 4 is an enlarged fragmentary view, partly in section, of the secondary coil-and-mandrel assembly produced by the second coiling operation;

FIG. 5 is a cross-sectional view through the secondary mandrel-and-coil assembly along the line V-V of FIG. 4, in the direction of the arrows;

FIG. 6 is a fragmentary side elevational view, partly in section illustration the tertiary coiling operation;

FIG. 7 is a fragmentary elevational view on an enlarged scale of the tertiary mandrel-and-coil assembly;

FIG. 8 is a fragmentary view of one turn of the finished cathode, the adjoining portions of the cathode being shown in dotted outline and the emission coating being omitted for convenience of illustration;

FIGS. 9 and 10 are elevational and cross-sectional views, respectively, of the loosely overwound core wire employed in the finished cathode shown in FIG. 8;

FIGS. 11 and 12 are views corresponding to FIGS. 2 and 3 but illustrate an alternative method of making an electrode according to the invention; and,

FIGS. 13 and 14 are views corresponding to FIGS. 9

and but illustrate the multiple-wire overwind produced by the alternative method.

While the present invention can be advantageously employed in the manufacture of various types of coiled electrodes that require a'plurality of coiling operations, it is especially adapted for use in fabricating triplewound cathodes fOr fluorescent lamps and it has, accordingly, been so illustrated and will be so described.

With specific reference to the drawing, in FIG. 1 there is shown a mount for a 212 watt 96" highly-loaded rapid-start fluorescent lamp. The mount is conventional design and, in general, consists of the usual glass flare 16 one end of which is pressed-sealed around a pair of lead wires 17 and 18. A heat-deflecting shield 19 is mounted on the press and connected to the lead wire 17. The ends of the lead wires that protrude from the stem press are fastened, as by clamping, to the ends of a triple-wound electrode 20 and to a pair of enlarged anodes 21 and 22 disposed on either side of the electrode. The primary and secondary turns of the electrode 20 are filled with a suitable electron-emissive material such as the well-known alkaline earth carbonates, applied in the usual manner, to activate the electrode and permit it to functiton as a cathode.

THE INVENTION The deformation and abrasion of the fine filamentary wire winding during manufacture is eliminated in accordance with this invention by winding a buffer wire of larger diameter simultaneously and in side-by-side relationship with the fine wire during the initial or primary coiling operation. This operation is illustrated in FIGS. 2 and 3. As there shown, a pair of primary wires consisting of a very fine wire or so-called filament wire 28 of tungsten and a buffer wire 30 of larger diameter and dissimilar metal, such as molybdenum, are wound in contingous side-by-side relation around a tungsten core wire 24 and a temporary filler wire 26 of molybdenum. The core wire is of smaller diameter than and is disposed in parallel longitudinally-extending paired relationship with the aforementioned filler wire to provide a composite primary mandrel. The paired fine filamentary and buffer wires are wound around the composite primary mandrel at a pitch such that the turns of grouped Wires lie next to one another, as shown in FIG. 2. The tungsten core wire and filler wire together with the tight overwinding of paired filament and buffer wires constitute a first multiple-strand or composite wire 23, as indicated by the bracket in FIG. 2. This initial coiling operation can very readily be performed on a continuous-winding type coiling machine that has been modified to include two rather than the usual single bobbin.

Alternatively, instead of winding the fine filamentary wire 28 and butter wire 30 simultaneously around the composite primary mandrel as above described, the filamentary wire could be wound first in the conventional manner and the buffer wire wound later, or even on another coil-winding machine. Thus, the invention includes within' its scope both the simultaneous and sequential winding of the additional bufier wire 30.

' Moreover, the tungsten core wire 24 does not necessarily have to be smaller than the filler wire 26 as here shown, but may be of the same diameter as or even larger than filler Wire, depending upon the electrode design, etc.

As indicated in FIGS. 2 and 3, the diameter of the buffer wire 30 exceeds that of the fine filamentary wire 28 by a distance d. The filamentary wire winding is, accordingly, recessed behind the buffer wire Winding a corresponding distance and is thus protected from abrasion during the subsequent coiling operations hereinafter described.

After the initial or primary winding operation has been completed the resulting first composite wire 23 is wound, as by another continuous coil-winding machine, around a larger secondary molybdenum mandrel. This secondary coiling operation produces a second and much larger composite wire 42, which is indicated by the bracket in FIG. 4. As shown, the secondary mandrel 16 is larger than either the filler or core wire and the pitch of the secondary winding is such that there is a predetermined spacing between the turns of the first composite wire 23.

As shown more particularly in FIG. 5, the buffer wire 35 by virtue of its larger diameter protrudes beyond the fine filament wire 28 and prevents it from coming into contact with the secondary mandrel 36. The larger diametered buffer wire, accordingly, serves as a temporary bearing surface that completely eliminates the abrasion or flattening of the fine wire overwinding that would otherwise occur as the composite wire 23 is tightly wound around the secondary mandrel 36 during the secondary coiling operation.

The same protection of the fine filamentary winding 28 against abrasion is also afforded by the buffer wire 30 during the tertiary coiling operation, which is depicted in FIG. 6. As shown, the second composite wire 42 (that is, the first composite wire 23 and the secondary mandrel 36) is fed from a bobbin (not shown) through the holder 32 and coiling die 34 of another coil-winding machine and then over and around a guide 38, at which point it is wound around a third and considerably larger steel mandrel 44. In order to reduce friction between the second composite wire 42 and the coiling die 34 the guide 38 preferably comprises a minature or so-called micro-ball bearing that is free to rotate about a pin 40 secured to the holder. A detailed description of this type of coil feed assembly and a tertiary winding operation of this character is set forth in U.S. Patent No. 2,783,816 dated March 5, 1957, and owned by the assignee of the present invention.

As a result of the tertiary winding operation a triplewound or compound coil having at least one turn is formed. In the particular type of cathode 20 shown in FIG. 1, the coil has five major turns. This third coiling operation is preferably done on a retractable-type coilwinding machine wherein the mandrel 44 is mechanically withdrawn from the coil after it is formed, as indicated by the arrow in FIG. 6. By way of clarification, the convolution of the second composite wire 42 illustrated in broken outline in FIG. 7 corresponds to a single turn of the finished cathode 20 shown in FIG. 1.

As will be noted in FIG. 7, the differential (dimension d) between the diameter of the primary filament wire 28 and primary bufier wire 30 also serves to protectively isolate the fine filament wire from the retractable mandrel 44 during the tertiary coiling operation and eliminates any abrasion of the filament wire that would otherwise occur during this phase of manufacture. Since the outermost surface of the buffer wire will always protrude beyond that of the fine wire, the latter will always be protected from damage regardless of how many coiling operatrons are performed.

After the compound coil is formed it is cut from the uncoiled portion of the composite wire 42 while the coil is still on the tertiary-winding machine. The resulting partly-fabricated electrodes at this stage of fabrication are of the same size and configuration as the finished cathode 20, except that they still contain the molybdenum filler wire 26, buffer wire 30 and secondary mandrel 36 and are not coated with emission material.

The aforementioned partly-fabricated electrodes are then further processed by annealing them in dry hydrogen for about 10 minutes at about 1200 C. in order to set the various windings in place on the mandrels. The electrodes are then immersed in a suitable solution that dissolves molybdenum, such as a mixture of nitric and sulfuric acids, to remove the filler and buffer wires and the secondary mandrel. Since the latter are all fabricated from molybdenum they are all removed in a single operation. The first composite wire 23 is thus converted into an entirely different composite wire 23' consisting of the the primary composite mandrel.

tungsten core wire 24 and a loose overwind of tungsten filament wire 28, as shown in FIG. 8. The turns of the finished cathode 20, part of which is illustrated in this figure, accordingly consists of a continuous triply-coiled filament wire supported by a heavier doubly-coiled core -wire that extends through the convolutions of the filament wire.

The basic structure of the wire 23' that forms the finished electrode is shown in greater detail in FIGS. 9 and 10. As shown, the removal of the filler wire 26 causes the tungsten filament wire 28 tobecome loosely draped around the tungsten core wire 24. This provides a basket-like structure capable of holding large amounts of emission material. The removal of the interposed buffer wire 30 from the fine wire winding spaces the turns of the latter a uniform distance apart, as denoted by the dimension S in FIG. 9. The buffer wire thus serves the dual purpose of eliminating abrasion defects in the finished electrode and maintaining a very uniform spacing between the turns of the fine wire filament or overwind. 1

It should be noted that the partly-fabricated electrodes, that is, those containing the molybdenum filler and butter wires and secondary mandrel, may be shipped in this form from the coil-winding department to the factory or the lamp manufacturing department where the final dissolving operation can be performed. The term partlyfabricated electrode as here used refers to the compound coils produced by thetertiary-coiling operation. At this stage of fabrication these compound coils comprise the fine filamentary wire 28 and larger buffer wire 30 disposed in side-by-side relation and wound into a tight coil that is, in turn, wound into a second and larger coil which is then wound into a third and still larger coil. The final coil still contains the molybdenum filler wire 26 which, together with the core wire 24, is located within and extends through the turns of the first coil. The secondary molybdenum mandrel 36 isalso still in place within and extends through the turns of the second coil.

I Specific example Following is a specific example of a cathode of the type used in a 212 watt 96" highly-loaded fluorescent lamp 1 inches in diameter operating at 1.5 amp. arc current which will illustrate in greater detail how this invention may be practiced. In this particular case a 1 mil tungsten filament wire 28 and a 1.5 mil molybdenum butter wire 30 are wound in paired relation around a 5.3 mil tungsten core wire 24 and a 10 mil molybdenum filler wire 26 at about 380 turns per inch (t.p.i.). The resulting composite wire was then wound around a 13 mil secondary molybdenum mandrel 36 at about 42 t.p.i. The resulting second composite wire was then wound around a steel retractable mandrel 50 mils in diameter at about 17 to 21t.p. i.

ALTERNATIVE EMBODIMENT It has been found that the amount of buffer wire required per electrode can be drastically reduced and the primary winding speed can be greatly increased by properly combining one butter wire with two fine filamentary wires and winding all three wires simultaneously around This embodiment is illustrated in FIGS. 11 and 12 and; as there shown, consists of locating the larger diametered buffer wire 30a between and in contiguous side-by-side relation with a pair of tungsten filament wires 28a and 28b and winding all three wires as a group around the paired tungsten core wire 24a and the larger molybdenum filler wire 26a to form a first composite wire 45. This group of three primary wires is wound around the composite primary mandrel at about half the turns per inch compared to that at which the pair of primary wires were wound in the first embodiment so that a predetermined spacing S exists between adjacent turns of the grouped primary wires, as shown in FIG. 11. Preferably, the spacing S is made approximately equal to the diameter of the bufferwire 30a so that each of the filamentary tungsten wires are spaced equal distances from each other in the finished electrode.

Once again, the buffer wire 30a may be wound separately during the primary winding operation 'on the same or another coil-winding machine.

The composite wire 45 produced by the aforementioned first coiling operation is then subjected to the secondary and tertiary coiling operations and finally the dissolving operation as described above in connection with the first embodiment. Y

The basic structure of the wire 45' in the finished electrode produced in .accordance with this embodiment is illustrated in FIGS. 13 and 14. As shown, the tungsten core wire 24a is loosely overwound with the pair of fine tungsten filamentary wires 28a and 28b, the adjacent turns whereof are spaced from one another a uniform distance S,,. The distance X between adjacent turns of the same tungsten wire is equivalent to twice the diameter of the buffer-wire 30a plus the diameter of the filamentary wire, as will be obvious from FIGS. 11 and 13. This uniform spacing is obtained by making the spacing S between turns of the three-wire primary grouping approximately equal to the buffer wire diameter.

When the filler wire 26a and buffer wire 30a are dissolved out of the coil the pair of fine tungsten filamentary wires 28a and 2812 are loosely draped around the core wire 24a, as shown in FIGS.'13 and 14. Thus, the basic structure of the wire 45' in the finished coil is identical to that produced with an overwinding of a single tungsten wire, except that two fine wires encircle the core wire at about twice the pitch. The filamentary tungsten wires are connected in parallel with one another when mounted on the lamp stern by the shunting effect of the lead wire clamp. The electrical resistance of this type electrode is, accordingly, lower than when a single filamentary wire is used.

It will be noted that since only one bufier wire is used for each pair of filamentary tungsten wires only half as much buffer Wire is required per coil as when one buffer wire is used for each filamentary wire. In addition, since the three wires are wound at twice the pitch the primary winding speed is doubled. Thus, combining one buffer wire with a pair of filamentary tungsten wires in accordance with this form of the invention not only provides a finished electrode with improved electrical characteristics but also effects a substantial cost reduction by decreasing the amount of buffer wire required and by increasing the rate of production.

As will be obvious to those skilled in the art, the required number of primary wires can very readily be wound simultaneously around the primary mandrel simply by increasing the number of bobbins and wire guides on the coil-winding machine.

II. Specific example Following is a specific example of the wire sizes and coiling data for a particular type coil further illustrating the above-described alternative embodiment.

Satisfactory 212 watt coils for a rapid-start highlyloaded fluorescent lamp 8 'feet long and 1 /2 inches in diameter have been made'according to this method by' simultaneously winding a pair of filamentary tungsten wires 1 mil in a diameter and a 1.5 mil molybdenum buffer wire as a group in side-by-side contiguous relation around a paired 5.3 mil tungsten core wire and a 10 mil molybdenum filler wire. The filamentary-butter wire grouping was wound at t.p.i. The resulting composite wire was then wound around secondary tertiary mandrels of the same sizes and in the same fashion as set forth above in the first specific example.

The term pitch as used in this description refers to the distance between identical points on adjacent turns of a given coil and is equal to 1/t.p.i.

p In summary, the objects of the invention have been achieved insofar as a novel Composite Wire has been provided which includes a fine filamentary wire and can be wound into a multiply-coiled electrode without abrading or otherwise damaging the fine wire winding. The improved composite wire also maintains -a very uniform spacing of the fine wire turns and can be very easily modified to effect a considerable reduction in manufac-- turing costs. There has also been provided a wire coil that contains the buffer wire component of this invention and can be conveniently and quickly converted into a finished multiply-coiled fluorescent lamp electrode ready for mounting.

While several examples of the compound wire and resulting intermediate or partly-fabricated electrode coil have been described in detail, various structural modifications may be made without departing from the spirit and scope of the invention.

I claim: 1

1. A composite Wire adapted for use in making a multiply-coiled electrode, said composite wire comprising a filament wire and a buffer wire of dissimilar metal that is disposed in side-by-side relationship with said filament wire and wound together therewith around a core wire, said buffer wire being larger in diameter than said filament Wire and protruding therebeyond a distance sufficient to protect the filament wire from abrasion during subsequent coiling operations.

2. The composite wire set forth in claim 1 wherein said filament wire is composed of tungsten and said buifer wire is composed of molybdenum.

3. An article of manufacture comprising: a fine wire and a Wire of larger diameter and dissimilar metal disposed in side-by-side relation and wound into a first coil that is, in turn, wound into a second and larger coil; a core wire and a filler wire located within and extending through the turns of said first coil; a mandrel located within and extending through the turns of said second coil; said mandrel and said second coil being wound into a third and still larger coil having at least one complete turn.

4. An article of manufacture comprising: a pair of fine wires and a wire of larger diameter and dissimilar metal that is located between and in side-by-side relation with said fine wires and wound together therewith into a first coil; said first'coil, in turn, being wound into a second and larger coil; a core wire and a filler wire located within and extending through the turns of said first coil; a mandrel located Within and extending through the turns of said second coil; said mandrel and second coil being wound into a third and still larger coil having at least one complete turn.

5. An article of manufacture comprising: a tungsten filament wire and a molybdenum buffer wire of larger diameter disposed in side-by-side relation and wound into a first coil that is, in turn, wound into a second and larger coil; a tungsten core wire and a molybdenum filler wire located within and extending through the turns of said first coil; and a molybdenum mandrel located within and extending through the turns of said second coil and comprising therewith a composite wire that is, in turn, wound into a third coil that is larger than said second coil and has at least one turn.

6. An article of manufacture comprising: a pair of tungsten filament wires and a molybdenum buffer wire of larger diameter that is located between and disposed in side-by-side relationship with said filament wires and is wound together therewith into a first coil; said first coil, in turn, being wound into a second and larger coil; a tungsten core wire and a molybdenum filler wire located within and extending through the turns of said first coil; a molybdenum mandrel located within and extending through the turns of said second coil and comprising therewith a composite wire that is, in turn, wound into a third coil that is larger than said second coil and has at least one turn.

References Cited by the Examiner UNITED STATES PATENTS 2,067,746 1/1937 Zabel 29423 2,218,345 10/1940 Spaeth 14071.5 2,306,925 12/1942 Aicher 14071.5 2,359,302 10/1944 Curtis 2925.15 2,516,930 8/1950 Varian 29423 DAVID L. RECK, Primary Examiner. 

1. A COMPOSITE WIRE ADAPTED FOR USE IN MAKING A MULTIPLY-COILED ELECTRODE, SAID COMPOSITE WIRE COMPRISING A FILAMENT WIRE AND A BUFFER WIRE OF DISSIMILAR METAL THAT IS DISPOSED IN SIDE-BY-SIDE RELATIONSHIP WITH SAID FILAMENT WIRE AND WOUND TOGETHER THEREWITH AROUND A CORE WIRE, 